Conventional housings for use with rolling element bearings have, up until now, broadly uniform radial stiffness. Hence the resultant load path, that is the portion of the outer or inner bearing ring raceway onto which the rolling elements contact and transmit the load to or from the inner ring raceway, is positioned over one part of the periphery of the outer ring or inner ring raceway when the bearing is subjected to a radial load.
The use of a single load path is the hitherto commonly accepted load pattern and all the current bearing performance predictions are based on this assumption. However, disadvantages arise with a single load path arrangement particularly in situations which require the bearing to provide lateral stiffness (that is stiffness across the axis of the bearing) and where vibration free operation is required.
The current practice is to attempt to achieve these requirements by introducing a degree of pre-load into the bearing, that is, to at least remove all clearance between the rolling elements and the respective inner and outer ring raceways.
To obtain an optimum degree of pre-load within a bearing can be difficult, time consuming and costly with the desired result not being fully achieved as basically a single active load zone still exists for carrying the radial load. This method is in the main a compromise condition and the degree of pre-load is uncertain and difficult to maintain.
Patent specification No. GB-A-2008451 (Georg Fischer) discloses a bearing assembly which utilizes a dry running bearing having pads which are continuously adjustable by means of an hydraulic flow and control circuit to vary the pre-load. This manner of pre-loading to achieve stability of the shaft is used where the subsequent movements are small in magnitude and/or slow in speed.
In other more dynamically demanding applications, clearance with the bearing surfaces are necessary to accommodate expansion of the components resulting from the heat generated within the bearing from the loads carried and the speed of operation. GB-A-2008451 cannot provide the requirements of lateral stiffness and vibration free operation in these dynamically demanding applications, besides being a complicated and expensive system.
Patent specification No. JP-A-62-124317 (Application No. 60-262531) (Shinano) uses s ring between an outer ring of a ball bearing and the bore of a housing, which ring has two radially inner projections. However, this ring is made of an elastomer such as rubber and in the dynamically demanding applications envisaged would not provide the requirements of lateral stiffness and vibration free operation.